The imagination of new worlds represented in science fiction cinema is a fertile ground for reflecting on the nature of international law. Assumptions of international law can be further tested by stretching their conditions of operation. International law’s argumentative structure makes it quite flexible, maybe more flexible than first appears. Concepts such as State, territory or even humanity seemingly central to the nature of international law can be fundamentally altered or even removed; a recognizable form of international law continues to operate. Still, fidelity to some features of the liberal ethos is needed for international law to continue being relevant. What sci-fi cinema proves is that the ideology of international law is embedded not in States, not even in humanity, but in the equality of rights of groups displaying enough anthropomorphic features. The disappearance of these features marks the end of the explanatory power of the international law analogy. In-between these extremes, science-fiction cinema can further provide relatable materials to make us think radically about international law.